hypodermic needle; injection needle
Refers to the needle used for injections, typically in medical contexts.
看護師が注射針を準備した。
The nurse prepared the hypodermic needle.
注射針を捨てる専用の容器がある。
There is a special container for disposing of injection needles.
注射器 refers to the whole syringe device, while 注射針 refers specifically to the needle attached to it.
Compound of 注射 (injection) + 針 (needle).